The present invention is directed to anti-centrifugal power chucks and, in particular, to chucks of the type having a plurality of radially-movable jaws and respective wedge-like actuators associated therewith for the purpose of displacing the jaws into engagement with a workpiece for holding same as the chuck is rotated at high speeds.
As noted in U.S. Pat. No. 4,123,075, of which the present inventor is a co-inventor, a long-standing problem with regard to the use of chucks which rotate at high speeds is the problem of the centrifugal forces that are developed on the jaws of the chuck, which centrifugal forces may significantly change the gripping force applied by the jaws to the workpiece. Furthermore, as also noted in this prior patent, the centrifugal force problem is particularly important with regard to chucks that are used for exteriorally gripping workpieces since it results in a reduction in the force by which the chuck grips the workpiece, and can result in slipping of the workpiece at relatively high rotational speeds.
To avoid this problem without the use of complex levers or other movable mechanisms for balancing the chuck, a sleeve-encased jaw chuck is disclosed in U.S. Pat. No. 4,123,075 which radially-slidably supports the jaw carriers within an inner sleeve-like body and utilizes an outer sleeve-like body (which closely confines the inner body and slidably engages wedge-like actuators) for preventing the centrifugal force imposed on the jaw carriers from causing any substantial reduction in the gripping force.
Additionally, the above-noted patent seeks to avoid another problem which has limited the efficiency of jaw chucks that utilize a cam or wedge structure for displacing the gripping jaws, namely, the problem of friction and wear imposed as a result of substantial twisting or turning moments applied to the jaw carrier. In particular, this is attempted by providing the jaw carrier with a central slot extending radially therethrough that accommodates the forward end of the actuating wedge to permit the force transfer between the jaw carrier and the wedge to occur within the central portion of the jaw carrier. Additionally, the wedge plate is removably mounted on the jaw carrier so as to enable it to be replaced once it has experienced substantial wear without requiring replacement of the complete jaw carrier assembly.
Although a very advantageous construction, the sleeve-encased jaw chuck of U.S. Pat. No. 4,123,075 has not been completely satisfactory in avoiding either of the noted problems for certain operating conditions. Since this chuck is operated by drawing the wedges away from the jaws, so as to pull the jaws radially inward, the wedge members are not backed up, at all times, by the chuck body itself nor any other element, so that the axially-outer, forward end of the jaws have a tendency to twist radially-outwardly away from the workpiece. Additionally, since the wedge members are only supported at a small portion of the outer sleeve-like body, and the outer sleeve-like body is not integral with the inner sleeve-like body, and since the sleeve-like body is relatively thin in the area of contact with the wedge members, the sleeve-like outer body is unable to exert sufficient force to resist the centrifugal forces which are imposed at high speeds. In fact, tests have established that, under certain circumstances, the outer sleeve-like body separates from the inner body under high rotational speeds to form a tri-lobed configuration, and, due to the resulting lack of support, outward movement of the gripping jaws and workpiece slippage.
Similarly, because of the above-noted twisting, resulting from the lack of full support for the jaws as they are brought into engagement with a workpiece due to withdrawal of the wedge members, and due to the rectangular shape of the interengaging portions of the wedge guiding slot and wedge member, the problem of wedge binding and associated wear due to twisting may cause difficulties under certain conditions.
The present invention contemplates providing a jaw-type chuck which will resist the centrifugal forces which are applied at high rotational speeds to a significantly greater degree than has been heretofore possible.
It is another object of the present invention to provide a construction of a multi-jaw chuck which will reduce the problems of binding and wear associated with the use of wedge-type actuators, without compromising strength.
It is another object of the present invention to provide a multi-jaw chuck which will operate satisfactorily for both external and internal gripping of workpieces. In addition to counteracting the effects of centrifugal force which would otherwise tend to release the gripping effect on externally gripped parts the chuck construction also prevents the centrifugal force effects from unduly increasing the gripping of thin walled tubes when it is used for internal gripping of such tubes.
Yet another object of certain aspects of the invention is the provision of a chuck construction which protects against the jaws breaking through the chuck periphery in the event of certain types of machine breakages.
These objects are achieved in accordance with a preferred embodiment of the present invention by integrating the inner and outer sleeve bodies of a chuck of the type shown in U.S. Pat. No. 4,123,075 into a unitary one-piece solid steel body. Furthermore, by modifying the wedge actuation system so as to operate under compression instead of tension for external gripping, greater support for the jaws is provided, and advantage can be taken of the basic fact that chuck construction materials are stronger in compression than they are in tension. Additionally, by utilizing a wedge member of cylindrical design, radial and circumferential support for the wedge member is increased, and problems of wedge binding due to twisting thereof is minimized. That is, while a rectangular slot will provide only a single planar surface to absorb all of the forces imposed radially-outwardly by the jaws and, thus, has a tendency to elongate radially-outwardly, a slot of circular cross-section provides a support surface of greater effective length than a comparable sized rectangular slot and distributes the loads in a variety of circumferential and radial directions. Furthermore, minimal binding can occur due to twisting of a circular cross-sectional solid member within a slot of circular cross-section in comparison to a rectangular solid twisted within a slot of rectangular cross-section.
An additional advantage of the above-noted use of a cylindrical wedge member is that substantial cost savings and simplification of manufacturing processes can be achieved since a cylindrical or part cylindrical hole can be cheaply and easily produced by drilling, particularly in a solid body, while more complicated procedures are required for production of a rectangular slot. Coupled with the reduction in parts achieved by the construction of the present invention relative to that of the prior art, the result is a stronger, and significantly less costly anti-centrifugal chuck which is not prone to the above-discussed problems.
Yet aother advantage of preferred embodiments of the invention is that the firm anti-centrifugal force arrangement protects against overgripping and distortion of internally gripped parts such as thin walled tubes.
A still further advantage of preferred embodiment of the invention is that all master jaw components are completely radially surrounded by the basic chuck body with no radial jaw slots cut through the chuck body periphery. With this arrangement, should any breakage occur internally due to machine wreckage or the like, all internal parts including the master jaws would be captivated within the basic chuck body providing additional operator safety.